Internal combustion engines (engines) produce mechanical power in the form of torque and rotational speed by combusting a mixture of air and fuel within one or more combustion chambers. During combustion, various exhaust gases are produced. A portion of the exhaust gas can be recirculated back into the engine cylinders (via an exhaust gas recirculation system). The recirculated exhaust gas can displace an amount of combustible mixture in the cylinder resulting in increased engine efficiency and lower combustion temperatures. The recirculated exhaust gas can reduce the combustion temperature in the cylinder and/or reduce formation of certain gaseous byproducts.
During start-up or initial warm-up of the engine, recirculation of the portion of the exhaust gas back to the engine cylinders may not be desired, and therefore, a three-way valve can divert this exhaust gas out through an aftertreatment device including via a turbocharger. When the engine is warmed up, the three-way valve can divert the portion of the exhaust gas back to the engine to recirculate this exhaust gas into the engine cylinders.
Internal combustion engines may be employed to generate considerable levels of power for prolonged periods of time. Many such engine assemblies employ an air compressor device, e.g., a turbocharger or a supercharger to compress the airflow before it enters the intake manifold of the engine in order to increase power and efficiency. By way of example, a turbocharger is a turbine device driven by exhaust pressure that includes a centrifugal gas compressor that forces air into the combustion chambers of the engine at pressures that are greater than ambient atmospheric pressure. The additional mass of oxygen-containing air that is forced into the engine improves the engine's volumetric efficiency, allowing it to burn more fuel in a given cycle, and thereby produce more power. Generally, the turbocharger is disposed upstream of the aftertreatment device.